1. Technical Field
The present disclosure relates to semiconductor devices. The present disclosure further relates to heterojunction bipolar transistors.
2. Description of the Related Art
Lateral heterojunction bipolar transistors (HBT) can be formed by depositing the emitter, base and/or collector contacts by plasma-enhanced chemical vapor deposition (PECVD) of hydrogenated silicon (Si:H) containing materials. Although the access resistance of the HBT devices can be sufficient for applications in large-area electronics, the access resistance of the devices can be too high for applicability to very large scale integration (VLSI) applications. Doping the emitter region and the collector region underneath the PECVD deposited contact regions can reduce the access resistance, and/or increase the current gain of the bipolar transistor by reducing the effective base width. However, high temperatures are required for activating the doping incorporated by ion implantation and/or for the diffusion of dopants. Furthermore, high temperature activation of the doped regions may create defects in the semiconductor material, resulting in undesired doping diffusion and junction widening. Further, in some applications where thin layers of semiconductor material is transferred and bonded onto low-cost flexible substrates, the high temperatures required for implantation/activation and/or diffusion is incompatible with low-cost flexible substrates.